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41.
In urban drainage systems, knowledge of short-duration rainfall events can be considered as one of the most critical elements when their hydrological behaviour wants to be investigated. The temporal resolution of rainfall data usually available for practical applications is often lower than the data requested for the design procedures or mathematical models application, greatly affecting their reliability. Moreover, when high resolution rain gauges are available in the catchment, the registration period cannot be sufficiently long for obtaining practically usable statistical analyses. The present study proposes a method for estimating the distribution of sub-hourly extreme rainfalls at sites where data for time interval of interest do not exist, but rainfall data for longer duration are available. The proposed method is based on the “scale-invariance” (or “scaling”) theory whose concepts imply that statistical properties of the extreme rainfall processes for different temporal scales are self-related by a scale-changing operator involving only the scale ratio. The methodology is applied to extreme rainfall data from a rain gauge network within the metropolitan area of Palermo (Italy). Following the application, it is shown that the statistical properties of the rainfall series have a simple scaling property over the range of duration 10 min–24 h. A simple parsimonious analytical formulation for the DDF curves, which embodies the scaling behaviour, is presented. 相似文献
42.
Germán Poveda 《Advances in water resources》2011,34(2):243-256
Diverse linear and nonlinear statistical parameters of rainfall under aggregation in time and the kind of temporal memory are investigated. Data sets from the Andes of Colombia at different resolutions (15 min and 1-h), and record lengths (21 months and 8-40 years) are used. A mixture of two timescales is found in the autocorrelation and autoinformation functions, with short-term memory holding for time lags less than 15-30 min, and long-term memory onwards. Consistently, rainfall variance exhibits different temporal scaling regimes separated at 15-30 min and 24 h. Tests for the Hurst effect evidence the frailty of the R/S approach in discerning the kind of memory in high resolution rainfall, whereas rigorous statistical tests for short-memory processes do reject the existence of the Hurst effect.Rainfall information entropy grows as a power law of aggregation time, S(T) ∼ Tβ with 〈β〉 = 0.51, up to a timescale, TMaxEnt (70-202 h), at which entropy saturates, with β = 0 onwards. Maximum entropy is reached through a dynamic Generalized Pareto distribution, consistently with the maximum information-entropy principle for heavy-tailed random variables, and with its asymptotically infinitely divisible property. The dynamics towards the limit distribution is quantified. Tsallis q-entropies also exhibit power laws with T, such that Sq(T) ∼ Tβ(q), with β(q) ? 0 for q ? 0, and β(q) ? 0.5 for q ? 1. No clear patterns are found in the geographic distribution within and among the statistical parameters studied, confirming the strong variability of tropical Andean rainfall. 相似文献
43.
44.
Igor A. Beresnev 《Journal of Seismology》2009,13(4):433-436
Attempts to build a “constant-stress-drop” scaling of an earthquake-source spectrum have invariably met with difficulties.
Physically, such a scaling would mean that the low-frequency content of the spectrum would control the high-frequency one,
reducing the number of the parameters governing the time history of a shear dislocation to one. This is technically achieved
through relationships of the corner frequency of the spectrum to the fault size, inevitably introduced in an arbitrary manner
using a constant termed “stress drop”. Throughout decades of observations, this quantity has never proved to be constant.
This fact has fundamental physical reasons. The dislocation motion is controlled by two independent parameters: the final
static offset and the speed at which it is reached. The former controls the low-frequency asymptote of the spectrum while
the latter its high-frequency content. There is no physical reason to believe that the static displacement should predetermine
the slip rate, which would be implied if the “stress drop” were constant. Reducing the two parameters to just one (the seismic
moment or magnitude) in a “scaling law” has no strict justification; this would necessarily involve arbitrary assumptions
about the relationship of one parameter to the other. This explains why the “constant-stress-drop” scaling in seismology has
been believed in but never reconciled with the data. 相似文献
45.
Hack's law was originally derived from basin statistics for varied spatial scales and regions.The exponent value of the law has been shown to vary between 0.47 and 0.70,causing uncertainty in its application.This paper focuses on the emergence of Hack's law from debris-flow basins in China.Over 5,000 debris-flow basins in different regions of China with drainage areas less than 100km2 are included in this study.Basins in the different regions are found to present similar distributions.Hack's law is derived fi'om maximum probability and conditional distributions,suggesting that the law should describe some critical state of basin evolution.Results suggest the exponent value is approximately 0.5.Further analysis indicates that Hack's law is related to other scaling laws underlying the evolution of a basin and that the exponent is not dependent on basin shape but rather on the evolutionary stage.A case study of a well known debris-flow basin further confirms Hack's law and its implications in basin evolution. 相似文献
46.
LI Yong YUE Z. Q. LEE C. F BEIGHLEY R. E. CHEN Xiao-Qing HU Kai-Heng CUI Peng 《国际泥沙研究》2009,24(1):74-87
Hack's law was originally derived from basin statistics for varied spatial scales and regions. The exponent value of the law has been shown to vary between 0.47 and 0.70, causing uncertainty in its application. This paper focuses on the emergence of Hack's law from debris-flow basins in China. Over 5,000 debris-flow basins in different regions of China with drainage areas less than 100km^2 are included in this study. Basins in the different regions are found to present similar distributions. Hack's law is derived from maximum probability and conditional distributions, suggesting that the law should describe some critical state of basin evolution. Results suggest the exponent value is approximately 0,5. Further analysis indicates that Hack's law is related to other scaling laws underlying the evolution of a basin and that the exponent is not dependent on basin shape but rather on the evolutionary stage. A case study of a well known debris-flow basin further confirms Hack's law and its implications in basin evolution. 相似文献
47.
中国主要陆地生态系统服务功能与生态安全 总被引:39,自引:0,他引:39
生态系统服务是国际生态学研究的前沿和热点,表现出向生态系统服务机理和区域集成方法两大方向发展的趋势.开展陆地生态系统服务研究,是生态系统恢复、生态功能区划和建立生态补偿机制、保障国家生态安全的重大战略需求.面向国家重大需求和生态系统服务研究的国际前沿,以主要陆地生态系统为对象,"中国主要陆地生态系统服务功能与生态安全"项目拟解决3个科学问题:①生态系统结构-过程-服务功能的相互作用机理;②生态系统服务功能的尺度特征与多尺度关联;③生态系统服务功能评估的指标与模型.通过上述研究,发展生态系统服务研究的理论与方法,为国家的生态建设和环境保护提供科学支撑. 相似文献
48.
Several fundamental issues of fracture mechanics during the post-dynamic stage are yet not fully understood, including fracture arrest mechanisms, effects of the three-dimensional fracture propagation on fracture aperture and height relations, and the role played by fracture tips on fracture termination. We studied these issues in the seismically active Dead Sea basin, where clastic dikes (>10 m) and numerous smaller dikelets (<1 m) dynamically intruded the late-Pleistocene soft rock of the Lisan Formation. A three-dimensional study of the dikelets shows that they form arrest zones at the tips of the larger clastic dikes. Geometrically, the dikelets are divided into two parts: (1) the main dikelet, in which the aperture profile along the dikelet height is approximately elliptic; and (2) the elongated tip, in which the aperture profile along the tip height is approximately constant. The dikelet aspect ratio is defined as A/H, where A is dikelet aperture and H is dikelet height. A plot of A/H versus H describes power relations with two different zones: (1) Zone A, with a small variation of A/H, between 0.02 and 0.06, for dikelets in height range of 100–700 mm; and (2) Zone B, where the aspect ratio sharply increases to 0.23 in dikelets with heights less than 100 mm. We interpret that during deceleration, when the height of the elongated tip became greater than 1/10 of the dikelet height, inelastic conditions are dominant. Under these conditions, the fracture velocity decreases significantly and the dikelet aspect ratio increases. The present observations and analyses indicate that formation of elongated tips and dike (fracture) segmentation are essential for the decay of the dynamic fracturing. 相似文献
49.
50.
恢复2009年1月1日-2015年12月31日间川滇活动块体中-北部1012次2.0≤M_L≤5.0地震的震源谱,计算标量地震矩M_o、震源尺度r和应力降△_σ等震源参数并拟合各参数间的定标关系,基于区域地震构造背景、活动断裂展布以及地震活动的成丛分布将研究区划分成四个统计单元,分别讨论各构造单元的应力分布特征、地震应力降随地点位置的变化以及应力-应变加载作用与区域变形的动力学过程的关联.结果显示:中小地震释放的应力降△_σ在0.1~10 MPa;标量地震矩M_o与近震震级M_L呈现较好线性关系(lgM_0=0.92M_L+10.46);应力降与地震大小的关系与Nuttli的增加应力降(ISD)模型比较吻合(1g△_σ=0.31 1gM_0-3.92).震源应力降结果显示:①金沙江断裂端部为低应力区,断裂单元整体滑动速率较高、强震活动极少,不具备强震发生的应力高度集中条件;在3条次级断裂构成的条带断裂结构中,理塘断裂上的应力-应变加载作用自北西向南东逐渐减弱,相对闭锁的北西段较其他部位更易积累应变.②鲜水河断裂带的地震应力降以康定为界南低北高,南段(康定-石棉)短期内难以积累较高应变,北段(甘孜-康定)应力水平较高,已发生的中强地震尚未能填充地震矩释放的亏空区,段落局部仍有较高的应力积累.③安宁河-则木河断裂上高应力降地震事件集中,该单元的应变积累强、应力水平最高,地震危险性大.④丽江—小金河断裂上不同震级地震的应力降特征并不相同,推测与当地复杂的构造背景有关,具体原因尚需深入探讨;木里地区应力背景较低,可能受当地构造环境的影响.研究表明,地震应力降随地点位置而系统变化,高应力降地震事件多发生在断裂与断裂的交汇部位,而断裂无闭锁条件、断裂以蠕滑为主且断面松弛、断裂端部为高温或破碎塑性变形带时,多以低应力降地震事件为主;与通常所认为的"走滑断裂不易积累应力"相反的是,鲜水河断裂带、安宁河—则木河断裂带均表现出较高的应力水平,其原因一方面可能是因为已发生的中强地震无论数量还是强度都尚不足以释放已经积累的能量,另一方面也许是在区域变形的复杂动力学过程中,当构造单元间阻碍断层运动和协助积累应力的作用占主导时,相同震级的地震会释放更多的应力. 相似文献